Breast Cancer Research and Treatment vol:118 issue:2 pages:425-432
Breast cancer is the most common female cancer in Europe, but its incidence and mortality are rapidly changing across Europe. The early termination of the women's health initiative (WHI) trial, after the detection of an increased breast cancer risk in hormone replacement terapy (HRT) users, was followed by strong declines of HRT use worldwide. We investigated whether the reduction of HRT sales affected breast cancer incidence in the Belgian province of Limburg. All women reistered in the Limburg cancer Registry with a diagnosis of invasive breast cancer diagnosed between1/1/1996 and 31/12/2005 were included in the study. Data on the use of HRT in the population were obtained from the vendors and the social security system. For age-standardization using the direct method, the European standard population was taken. In 2003 and 2004, the breast cancer incidence rate decreased significantly as compared to 2002 for women aged between 50 and 69 years. This sudden drop in the incidence intercepted a markedly increasing trend until 2002, but was followed again by an increase in 2005. Between 2002 and 2006, the sales of HRT (about 75% to women aged 50-69 years) were reduced by 41%. Breast cancer incidence was maimally related to HRT use in the provious year (R2 = 77%). The decrease of breast cancer incidence in the Belgian province of Limburg may largely be related to the fall of HRT use following the early termination of the WHI trial. This suggests that HRT stimulates the growth of preexisting, clinically latent tumours that may not otherwise become clinically apparent.